The present invention relates to airlock devices for feeding metered amounts of particulate material from a storage area into an adjacent chamber without allowing gas to flow between the storage area and the chamber. More specifically it relates to an airlock device for feeding particulate material into a pneumatic separator in which upwardly moving columns of air separate the particulate material into fractions according to density and/or aerodynamic properties. For efficient separation to occur in a pneumatic separator it is necessary that particulate material be fed into the separation chamber in continuous metered stream. The flow of material into the separator should be set at or below the maximum capacity of the separator, but should be as near the maximum as possible to assure maximum energy conservation.
In the past a constant flow of particulate material has been provided by a system which includes a surge bin with a metering flight conveyor and scalping roll. The conveyor would deliver particulate material to a vibrating feeder which in turn would deposit the material into an airlock feed device such as a rotary star feeder or the like. The airlock feed device served as a seal between the material storage area and the separation chamber. This system has proved to be disadvantageous in that it requires an excess of costly equipment which takes up a great deal of floor space.